The Decoder found it and it is not geometry: my leaf path pairs each pose with
the NEXT pose's time. Fed my pairing into its own interpolation it reproduces
-324 to the digit; corrected, t=355 gives centre 980.5 against 992.0 measured. So
there was no 1300 px pivot mystery, and saying both numbers rather than hunting
one is what surfaced it.
CORRECTING BLOCKED: this was never gated on a branch landing. The row said the
change "cannot be taken yet ... reaches the port only when that branch lands on
main". Wrong -- ui_layout.rs in this checkout carries the corrected association
behind SYLPHEED_KF_TIME_SHIFT=1 and has all along. I read that file twice this
session, once for rotation_deg and once for the leaf note, without noticing the
switch.
Ran the experiment. Re-exported under the shift and asked the oracle:
publisher_logo 1.00% -> 0.75% better
developer_logos 0.39% -> 0.33% better
title RMSE 21.07 -> 20.41 better (area 1.82 -> 1.86, worse)
main_menu 0.06% -> 0.10% worse
extras 0.20% -> 0.24% worse
NOT DECISIVE, and the reason is the point: under the shift the untimed keyframe
moves from LAST to FIRST, while `pose_at` is written around "the final keyframe
carries no t, so it is given a synthetic time exit_ramp_units after the last
timed frame". The numbers measure a renderer/association mismatch, not the
association. Adopting it means re-deriving exit_ramp_units, settle_units,
spin_period_units and the plate against a layout where the untimed frame is
first. Export reverted to the default; doing that work hastily is how a 1.8% gap
becomes five wrong ones.
THE METHODOLOGICAL POINT IS THE DECODER'S AND IS THE BEST THING HERE: its rule
matched because alpha at t=355 sits inside a long segment where a one-keyframe
shift barely moves it, while x sweeps 1560 px over the same span. It confirmed on
the insensitive quantity, I was wrong on the sensitive one, and neither of us saw
it until they were compared. CHECK A NEW INTERPRETATION AGAINST THE FASTEST-MOVING
FIELD YOU HAVE, NOT THE ONE THAT HAPPENS TO AGREE. That is a control chosen where
it could not fail, which is a different failure from the uncontrolled instruments
this session has collected.
An 11.5 px residual is left and is not to be fitted.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF
c602bb3c47